From 5f4e5752a8a3a72c79514def2ad9fc7cd410ce2e Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Mon, 19 Sep 2016 10:12:45 +1000
Subject: fs: add iomap_file_dirty

Originally-From: Christoph Hellwig <hch@lst.de>

This function uses the iomap infrastructure to re-write all pages
in a given range.  This is useful for doing a copy-up of COW ranges,
and might be useful for scrubbing in the future.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/iomap.c b/fs/iomap.c
index 706270f..e9b3f99 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -252,6 +252,88 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);
 
+static struct page *
+__iomap_read_page(struct inode *inode, loff_t offset)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct page *page;
+
+	page = read_mapping_page(mapping, offset >> PAGE_SHIFT, NULL);
+	if (IS_ERR(page))
+		return page;
+	if (!PageUptodate(page)) {
+		put_page(page);
+		return ERR_PTR(-EIO);
+	}
+	return page;
+}
+
+static loff_t
+iomap_dirty_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
+		struct iomap *iomap)
+{
+	long status = 0;
+	ssize_t written = 0;
+
+	do {
+		struct page *page, *rpage;
+		unsigned long offset;	/* Offset into pagecache page */
+		unsigned long bytes;	/* Bytes to write to page */
+
+		offset = (pos & (PAGE_SIZE - 1));
+		bytes = min_t(unsigned long, PAGE_SIZE - offset, length);
+
+		rpage = __iomap_read_page(inode, pos);
+		if (IS_ERR(rpage))
+			return PTR_ERR(rpage);
+
+		status = iomap_write_begin(inode, pos, bytes,
+				AOP_FLAG_NOFS | AOP_FLAG_UNINTERRUPTIBLE,
+				&page, iomap);
+		put_page(rpage);
+		if (unlikely(status))
+			return status;
+
+		WARN_ON_ONCE(!PageUptodate(page));
+
+		status = iomap_write_end(inode, pos, bytes, bytes, page);
+		if (unlikely(status <= 0)) {
+			if (WARN_ON_ONCE(status == 0))
+				return -EIO;
+			return status;
+		}
+
+		cond_resched();
+
+		pos += status;
+		written += status;
+		length -= status;
+
+		balance_dirty_pages_ratelimited(inode->i_mapping);
+	} while (length);
+
+	return written;
+}
+
+int
+iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
+		struct iomap_ops *ops)
+{
+	loff_t ret;
+
+	while (len) {
+		ret = iomap_apply(inode, pos, len, IOMAP_WRITE, ops, NULL,
+				iomap_dirty_actor);
+		if (ret <= 0)
+			return ret;
+		pos += ret;
+		len -= ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iomap_file_dirty);
+
 static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
 		unsigned bytes, struct iomap *iomap)
 {
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 3d70ece..3a56212 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -64,6 +64,8 @@ struct iomap_ops {
 
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		struct iomap_ops *ops);
+int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
+		struct iomap_ops *ops);
 int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
 		bool *did_zero, struct iomap_ops *ops);
 int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
-- 
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